New superconductor particle accelerator reaches temperatures below space on Earth

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The particle accelerator that knocks down electrons here on Earth has reached temperatures lower than in space.

Using x-ray free electron laser in the Department of Energy’s Department National Accelerator Laboratory SLAC– part of the Linac Coherent Light Source Modernization Project (LCLS), called LCLS II – scientists have cooled liquid helium to minus 456 degrees Fahrenheit (minus 271 degrees Celsius), or 2 Kelvin. This is just 2 kelvins above absolute zero, the lowest possible temperature at which any movement of particles stops. This frosty environment is crucial for the accelerator because at such low temperatures the machine becomes superconducting, which means it can push electrons through it with almost zero energy loss.

Even empty areas of space are not so cold, as they are still filled with cosmic microwave background radiation, remnants shortly after The big bang having a uniform temperature of minus 454 F (minus 271 C), or 3 K.

“The new-generation LCLS-II free-generation X-ray superconductor accelerator has reached operating temperatures 2 degrees above absolute zero,” said Andrew Baryl, director of the SLAC Accelerators Directorate, in an interview with Live Science.

The LCLS-II is now ready to start accelerating electrons at a rate of 1 million pulses per second, which is a world record, he added.

“It’s four orders of magnitude more pulses per second than its predecessor, LCLS, which means that in just a few hours we’ll be sending users more X-rays [who aim to utilize them in experiments] than LCLS has done in the last 10 years, ”Baryl said.

This is one of the last milestones the LCLS-II must achieve before it can produce X-ray pulses that are on average 10,000 times brighter than those created by its predecessor. This should help researchers explore complex materials in unprecedented detail. High-intensity, high-frequency laser pulses allow researchers to see how electrons and atoms in materials interact with unprecedented clarity. It will have a range of applications, from helping to identify “how natural and man-made molecular systems convert sunlight into fuel, and thus how to control these processes, to understanding the fundamental properties of materials that will allow quantum computing,” Buril said. .

Microwaves are pumped through cooled cavities, accelerating electrons almost to the speed of light. (Authorship: Greg Stewart / SLAC National Accelerator Laboratory)

Creating a frosty climate inside the accelerator required some work. For example, the team needed ultra-low pressure to keep the helium from boiling.

Eric Fowe, director of the cryogenic division at SLAC, told Live Science that at sea level pure water boils at 212 F (100 C), but that boiling temperature varies with pressure. For example, in a pressure cooker the pressure is higher and the water boils at 250 F (121C), while at an altitude where the pressure is lower and the water boils at a lower temperature, the opposite is true.

“For helium, it’s very much the same. At atmospheric pressure, helium will boil at 4.2 Kelvin; that temperature will decrease as the pressure decreases,” Fove said. “To lower the temperature to 2.0 Kelvin, we need to have a pressure of only 1/30 of atmospheric.”

To achieve this low pressure, the team uses five cryogenic centrifugal compressors that compress helium to cool and then allow it to expand in the chamber to lower the pressure, making it one of the few places on Earth where 2.0 K of helium can be produced on a large scale.

Fowe explained that each cold compressor is a centrifugal machine equipped with a rotor / impeller similar to a turbocharged engine.

“During rotation, the impeller accelerates helium molecules, creating a vacuum in the center of the wheel where the molecules are sucked in, creating pressure on the periphery of the wheel where the molecules are ejected,” he said.

The animation shows how a linear-type cryo-accelerator cools helium gas to a liquid phase.

The animation shows how a linear-type cryo-accelerator cools helium gas to a liquid phase. (Authorship: Greg Stewart / SLAC National Accelerator Laboratory)

Compression causes helium to go into a liquid state, but helium escapes into this vacuum, where it expands rapidly while cooling.

In addition to its end use, the supercold hydrogen created in LCLS-II is itself a scientific curiosity.

“At 2.0 Kelvin, helium becomes a superfluid called helium II, which has unusual properties,” said Fove. For example, it conducts heat hundreds of times more efficiently than copper, and has such low viscosity – or flow resistance – that it is impossible to measure, he added.

For LCLS-II 2 kelvins – this is as much as the expected temperature.

“Low temperatures can be achieved with the help of highly specialized cooling systems, which can reach a fraction of a degree above absolute zero when all movements stop,” Baryl said.

But this particular laser does not have the ability to reach these extremes, he said.

Originally published on Live Science.

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